None
Not applicable.
The excision of diseased or abnormal tissue from the body traditionally has been termed an xe2x80x9cinvasivexe2x80x9d one. In carrying out invasive surgery, medical practitioners generally have resorted to the use of sharpened edge tools and, for about six decades, additionally, forms of electrosurgery. In the latter regard, a somewhat pioneer electrosurgical device was developed by William T. Bovie. This early device, described, for example, in U.S. Pat. No. 1,813,902 issued on Jul. 14, 1931 entitled xe2x80x9cElectrosurgical Apparatusxe2x80x9d and its successors have met with acceptance over the years within the surgical community to the extent that current versions are referred to as the xe2x80x9cBoviexe2x80x9d.
For both traditional excision approaches, injury generally occurs to surrounding or peripheral and healthy tissue. While certain of such injuries are apparent, others have been reported which are more subtle. Conventional removal of malignant tumor, as well as more simple biopsy procedures have been reported to generate xe2x80x9cseedingxe2x80x9d or spreading or metastasizing cancer in the body. In addition to patient discomfort and longer recovery periods, more invasive surgical procedures are reported to be accompanied by a period of immunosuppression, a condition increasing the risk of disease spread. See the following publications in this regard:
xe2x80x9cImpaired Production of Interlukin-2 after Surgery,xe2x80x9d T. Akiyoshi, et al., Clin. Exp. Immunology, Vol. 59, pp 45-49, 1985.
xe2x80x9cThe Influence of Surgical Operations on Components of the Human Immune System,xe2x80x9d T. Lennard, et al., British J. of Surgery, Vol. 72, pp 771-776, 1985.
Less invasive alternatives to conventional surgical procedures have been and continue to be investigated, particularly as the clinical detection of tumor or tissue abnormalities has become more refined. For example, current imaging systems (mammography, ultrasonographs, MRI) may detect and locate very small tumor or tissue abnormalities sized at the level of a millimeter. Where such tumor is detected, for example, in the breast, biopsy procedures employing fine needle aspiration techniques may be utilized. Retrospective investigation, however, has determined that about 80% of such biopsied tissue is benign. Where malignancy is determined, the biopsy procedure risks the above-noted seeding or metastasization opportunities. Excision of even the smaller aberrant tissue zones typically is both traumatic to the patient and relatively cost intensive. The latter cost aspect also is present with conventional needle biopsy procedures.
Particularly where small tumors or tissue abnormalities are encountered, investigators have looked to potentially less invasive and thus less costly and less traumatic procedures. For example, if a smaller tumor can be biologically destroyed in situ so as to become ischemic or necrotic, the resultant small zone of dead tissue eventually will be physiologically eliminated by resorption.
One approach to carrying out an in situ destruction of such smaller targeted tissue zones has been to thermally affect the volume of aberrant tissue. Such an approach may involve either cooling or heating the target tissue to the point of irreversible cell death or necrosis. For the former, cooling approach, reference is made to following publication:
xe2x80x9cRequisites for Successful Cryogenic Surgery of Cancer,xe2x80x9d H. Neel, et al., Arch. Surg., Vol. 102, pp 45-48, 1971.
The latter approach, that of inducing therapeutic hyperthermia generally is a less invasive one. A rather broad variety of technical modalities have evolved to elevate the temperature of tissue. For example, biological tissue volumes may be heated by inductive, radiant, contact or joulean based techniques. While these hyperthermic approaches exhibit potential advantage over the highly invasive surgical modalities, limitations to their use have been identified. Inductively based systems, certain of which are described in U.S. Pat. Nos. 5,251,645 and 4,679,561 perform by passing high frequency electromagnetic radiation through tissue. This is achieved by passing the radiation between two external electrodes positioned adjacent the patient""s skin. A drawback of such an approach to therapeutic hyperthermia resides in the heating of a relatively large volume of tissue at elevated temperatures for extended intervals of time. Typically with this practice, tissue is heated to temperatures of 6xc2x0 C. to 10xc2x0 C. above normal body temperature for periods of twenty minutes or more to achieve necrosis. The systems generally do not allow the volume of tissue to be well defined, i.e., the treatment is inaccurate, resulting in either insufficient necrosis or excessive necrosis extending into surrounding healthy tissue. As a consequence, practitioners have looked to combining prolonged heating of tissue with chemotherapy or radiation therapy modalities.
Interstitial thermotherapy has become an important alternative to invasive surgical methods. In general, six thermotherapy modalities have been developed for heating or cooling tissue. They are identified as: (1) radiofrequency heating, (2) microwave heating, (3) laser heating, (4) ultrasound heating and (5) cryogenic cooling. Radiofrequency heating procedures are categorized as direct and indirect. The latter, indirect, approach involves the placement of metal wires or pellets (which may be autoregulated) in the target tissue and then externally applying an R.F. field.
The above six modalities involve either of two methods of temperature alteration in tissue, to wit, conduction and diffuse or distributed heating of targeted tissue. Conduction may be of heat from or to a device or instrument and is characterized as a slow process since thermal diffusion through tissue is a somewhat slow phenomenon. This can lead not only to longer treatment periods but uncertainty in the size and shape of the final lesion, again a problem of treatment accuracy. Such conduction-limited modalities include: indirect radiofrequency heating, laser heating, and cryogenic cooling. Conduction-limited therapeutic heating of tissue using radiant sources is described, for example, in U.S. Pat. Nos. 5,284,144; 4,872,458; and 4,737,628. Radiant sources, such as lasers, produce localized heating of tissue, but do not permit the affected volume to be predetermined, a priori. Other conduction-limited contact heating approaches have been used for inducing therapeutic hyperthermia as are described in U.S. Pat. Nos. 4,979,518; 4,860,744; 4,658,836; and 4,520,249.
Diffuse or distributed heating of targeted tissue is distinctly different from the above-described conduction-limited method. This approach has the potential advantage that the target tissue can be heated to a desired cauterization temperature within relatively shorter interval of time. Cauterization procedures involve bringing targeted tissue to a temperature within a predetermined temperature range for a duration resulting in irreversible cell death. However, while representing a procedure exhibiting much promise, investigators have encountered obstacles in its implementation. In this regard, the volume of tissue cauterized is generally more difficult to control for systems incorporating microwave or ultrasound procedures, inasmuch as these procedures depend upon the radiation of tissue-heating energy into a volume of tissue from an emitting transducer or antennae system. The precise size of any resulting lesion depends upon the duration of treatment as well as the microwave or ultrasound responsiveness of the targeted tissue. In this regard, investigators have looked to the placement of one or more temperature sensors within the treatment field or have looked to the measurement of electrical impedance to assess the extent of the volume of cauterized tissue to determine an end point termination of the therapy. The problem of treatment accuracy again is posed. See generally, U.S. Pat. Nos. 5,122,137; 4,776,334; and 4,016,866. A direct measurement of tissue impedance is described, for example, in U.S. Pat. Nos. 5,069,223 and 4,140,109. These procedures are complex and somewhat costly. Of the diffuse or distributed heating approaches, electrosurgical techniques hold promise for both precise and predictable cauterization of targeted tissue volume, as well as a rapidity of the treatment process. Devices and technology representing this category are described, for example, in U.S. Pat. Nos. 5,728,143; 5,683,384; 5,672,173; 5,672,174; 5,599,346; 5,599,345; 5,486,161; 5,472,441; 5,458,597; 5,536,267; 5,507,743; 4,486,196; 4,121,592; and 4,016,886. See also, PCT Application WO 96/29946.
Electrosurgical instruments generally perform in either of two operational modes, monopolar or bipolar. In the monopolar mode, electric current is conducted between a relatively small active electrode and a large return electrode located a distance from the active electrode. Because in the monopolar mode, current density in tissue decreases as the square of the distance from the active electrode, it is more difficult to treat more than very minimal volumes of targeted tissue as well as to maintain the volumetric accuracy of such treatment. Notwithstanding such a surface related operational limitation, the monopolar devices are quite efficient as electrosurgical cutting tools and for the purpose of carrying out a coagulation at the surface of tissue being cut. Each approach involves a different waveform but both are surface related and involve a modicum of arcing between the instrument tip and the tissue being affected.
The bipolar mode of electrosurgical (joulean) heating involves passing current between tissue disposed between two electrodes of similar surface area. To effect cauterization of targeted tissue, this electrosurgical heating technique has been implemented with instruments which deploy pointed, flexible fine wire or needle-like electrode-functioning stylets directly into the targeted tissue. This calls for a mechanical system carrying out tissue penetration with these fine deployed stylets which necessarily will have a small surface area per unit length of the electrode. As a consequence, the permissible current flux flowing between the electrodes is significantly limited inasmuch as excessive current densities will cause desiccation of tissue immediately adjacent the electrodes which defeats the procedure. This follows, inasmuch as the desiccated tissue adjacent the electrode will then exhibit a very high electrical impedance which prevents further tissue heating and thus limits the volume of tissue which can be treated to the point of effective cauterization. For this reason, the fine needle or stylet techniques heretofore employed have been observed to require a treatment duration of ten to fifteen minutes for larger lesions. Further, a temperature monitoring of the fine electrode and even the infusion of conductive fluids is called for to reduce impedance between the electrodes and surrounding tissue. Additionally, practice with the needle extruding mechanisms have shown them to be difficult to deploy, the practitioner having less than desirable information as to the exact positioning of the fine electrode stylets. For example, these wires will deflect in the procedure of insertion into the targeted tissue in dependence upon their degree of flexibility as well as upon the varying density characteristics of abnormal tissue sought to be cauterized. Placement identification or observation procedures using conventional imaging systems is hindered because of the highly diminutive surface area of the electrodes themselves. In this regard, such imaging systems fail to xe2x80x9cseexe2x80x9d the electrodes. As a consequence, the targeted tissue is either under-treated or the treatment procedure extends cauterization excessively into adjacent healthy tissue, i.e., it encroaches excessively beyond the targeted tissue volume. Treatment accuracy again remains problematic. Bipolar mode electrosurgical procedures are described, for example, in U.S. Pat. Nos. 5,720,744; 5,403,311; 5,122,137; 4,920,978; 4,919,138; and 4,821,725, while fine needle electrode technologies are set forth, for example, in U.S. Pat. Nos. 5,470,309; 5,370,675; 5,421,819; 5,470,308; and 5,607,389.
Investigators also have looked to the destruction or control of tumor by the devitalization or vascular interruption of oxygen and nutrient ingress to targeted tissue volumes. Resultant cell death or necrosis again may be accompanied by its physiologically natural absorption by the body. As before, while this general approach to tumor management holds promise, the practical aspects of control over the targeted tissue volume using minimally invasive tactics has remained elusive. See generally; Denekamp et al., xe2x80x9cVascular Occlusion and Tumor Cell Death,xe2x80x9d Eur. J. Cancer and Clinical Oncology, Vol. 19 No. 2, pp 271-275 (1983).
As is essentially the case in all remotely guided procedures, the process for carrying out an incision for example, of a volume of targeted tissue is difficult. This difficulty is particularly in evidence where an incision is called for which does not invade the targeted tissue volume, extending only about its periphery.
Highly controlled and accurate RF electrosurgical cutting promises to enjoy a number of surgical applications beyond topics such as vascular isolation of tissue volume. For example, rather basic intravascular catheter guided monopolar electrodes have been employed as therapy for a variety of cardiac dysrhythmias. The therapy involves maneuvering of a monopolar electrode to sites of arrhythmogenic myocardium to carry out an ablation of heart muscle at discrete areas. While the therapy has demonstrated high therapeutic effectiveness, the treatment procedure is somewhat primitive, substantial volumes of tissue at the inner wall of the heart being destroyed until the aberrant conduction pathway is eliminated or blocked by the resultantly necrosed tissue. R. F. catheter ablation techniques also have been used to treat ventricular tachycardias, atrial flutter, ectopic atrial tachycardia, and sinus node reentry, albeit with lower success rates. These techniques are still evolving and, as is apparent, a technique for accurately forming a controlled linear lesion of known and minimal dimension will represent a beneficial advance in the therapy. See generally: Wood et al, Radiofrequency Catheter Ablation for the Management of Cardiac Tachyarrhythmias, Am J Med Sci 1993;306(4):241-247.
The present invention is directed to the system, apparatus and method for accurately cutting about and into tissue volumes with electrosurgically deployed electrodes. The electrode employed with the instrumentation is electrosurgically excited during the act of its deployment with respect to two, spaced apart support positions. By using two such positions, the instrument design takes advantage of the inherent structural integrity of the arch. To implement this approach, a thin, resilient elongate electrode is mounted within the forward end region of a support member such that its distal end is fixed to the instrument while it extends longitudinally rearwardly. Within the forward end region, the electrode extends within a deployment slot, the sides of which, in turn, extend between a forward location adjacent the instrument tip and a rearward location. The sides of the deployment slot in combination with a compression-based mounting arrangement serve as structurally supportive abutments to the arch formation developed as the electrode is outwardly deployed by urging it forwardly into a compression stabilized arch. Control over the extent of deployment is provided by the corresponding extent of the forward movement of the electrode. Thus a highly stable compressed electrode arch configuration is developed with a repeatable and reliable profile which is substantially immune from deformation which otherwise might occur during the carrying out of electrode cutting maneuvers pushing the sidewise extent of the electrode through tissue.
The accuracy and repeatability achieved with the instant system has important applicability to procedures for carrying out the circumscriptive vascular isolation of a targeted tissue volume such as a tumor. Because the arch shaped electrode is electrosurgically excited for cutting both during its deployment and retraction, a combination of those maneuvers with a relatively simple pivoting of the forward end region of the instrument permits the devascularization of such tissue to occur without the instrument touching that targeted tissue volume itself. With the system, typically a volume of targeted tissue such as tumor is isolated by a cut providing necrotic interfacing cut surfaces having a resultant circumscribing volume shape resembling a segment of an orange. A desirable repeatability of the geometric pattern cut with the system permits an iteration of the maneuvering procedure utilizing the coagulating output of the associated electrosurgical generator. Thus, the devascularization or dearterialization of the targeted tissue volume may be enhanced with beneficial elimination of any bleeding which might occur. Generally within minutes, the isolated targeted tissue volume will begin to experience cell death and over a period of time, the natural functioning of the body may resorb it.
The accurate cutting achieved also permits the very accurate positioning or deposition of a barrier within the interface defined by the circumscriptive cut carried out with the arch shaped electrodes. Such barriers will contribute to the assurance that the targeted tissue volume is fully isolated from surrounding vital or healthy tissues to an extent beneficially restricting the rate of any neovascularization in addition to the accurate positioning of barrier substances or fluids at the noted cut interface. The structurally robust mounting of the electrode configuration also permits it to draw a membranous barrier shroud through the cut interface to carry out the noted additional isolation of targeted tissue.
In the discourse to follow, the term xe2x80x9cbarrierxe2x80x9d is referred to in the description of a variety of instrumentation embodiments. Such barrier components may be chemical agents functioning to slow down a revascularization process by increasing the depth of necrotic tissue which such neovascularization must span. Necrotising agents are selected for suitable localized administration and may include chemotherapeutic agents as well as alcohol and the like. The term xe2x80x9cbarrierxe2x80x9d also is used in a physical sense to function to slow down revascularization through utilization of resorbable mesh or membranes, adhesives and various anti-adhesion barriers. A variety of barrier agents and devices are described in the discourse to follow.
The accuracy and stability of the electrode system also lends it utility to the electrosurgical treatment of atrial flutter. In this regard, rather than the relatively uncontrolled electrosurgical ablation procedures currently practiced, the arch shaped electrode can be incorporated at the tip of an intravascular heart catheter for positioning against the interior heart wall at a location transversely intercepting the current path of that reentry current intended to be interrupted. The electrode then is deployed while being electrosurgically excited to perform an accurate linear cut with cut tissue sides providing a necrotic tissue interface functioning to interrupt the current path in avoidance of atrial flutter. In effect, treatment is achieved with substantially reduced damage to the heart wall.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The invention, accordingly, comprises the method, system and apparatus possessing the construction, combination of elements, arrangement of parts and steps which are exemplified in the following detailed description.
For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings.